Human‐Polymorphonuclear‐Leucocyte Neutral Protease and Its Inhibitor

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Abstract
Human polymorphonuclear leukocytes were obtained from the synovial fluids of patients with inflamed knee joints suffering either from Reiter''s syndrome or from rheumatoid arthritis. The polymorphonuclear leukocytes were collected by gentle centrifugation followed by disruption and their subcellular fractionation by centrifugation in 0.34 M sucrose to provide a granule fraction and a post-granule supernatant fraction. 0.5 M KC1 extraction of the granule fraction yielded neutral protease activity, similar to trypsin, when assayed against fluorescein-labeled polymeric collagen fibrils. The post-granule supernatant fraction contained an inhibitor towards the neutral protease and trypsin. The inhibition of the neutral protease was time-dependent, this inhibition being released after 1.5-2 h. In contrast, the inhibition of trypsin was irreversible and this property was used to devise an assay procedure for the inhibitor.